boyd porcelain jar lid

[pault]

While diving in the Niagara River i came upon a milk glass lid marked Boyd's Genuine Porelain marked on the outter rim and in the center a square with an M in thinner more fluid script onthe reverse side is the number 24. I assume it is as canning jar lid but how can I find out how old it is>

 

[junkyard jack]

Yes, It is the porcelain liner from a zinc fruit jar lid.
Having the "M" inside a square (actually is a diamond), sounds like a lid for RB 10 #1624-1625 "The Marion Jar" Mason's Patent etc.
That lid dates to approx. 1890-1904 & in very good, complete condition is worth $15-20.